HDPE socket fittings are key accessories that are connected to HDPE pipes by hot-melt. They are widely used in municipal water supply and drainage, gas transportation, farmland irrigation, chemical transportation and other fields. The socket connection method has the advantages of compact structure, excellent sealing performance, and simple connection operation. Therefore, it is widely used in small and medium-caliber PE pipeline systems. In order to ensure the dimensional accuracy, mechanical properties and welding quality of the pipe fittings, it is crucial to choose the molding process reasonably.
Injection molding: the mainstream process of HDPE socket fittings
The most commonly used manufacturing method for HDPE socket fittings is the injection molding process. This process heats and melts the HDPE raw material and injects it into the mold cavity, and then takes out the finished product after cooling and shaping. Because HDPE material has good fluidity and thermal stability, it is particularly suitable for injection molding to manufacture complex shapes and high-precision pipe fittings.
The injection molding process is suitable for standardized socket connectors such as elbows, equal-diameter tees, reducing tees, pipe caps, and flange nipples. For PE socket fittings less than DN200, injection molding is the most economical, efficient, and ideal way for mass production.
Injection molding process
Raw material preparation: Select PE100 or PE80 raw materials that meet ISO 4427 or GB/T 13663 standards, and require uniform particles, no impurities, and low water content.
Melting plasticization: Heat the HDPE particles to 190℃~230℃ in the injection molding machine to reach a completely molten state.
Injection into the mold cavity: Inject the molten plastic into the cooling mold at high pressure (above 80MPa) through the screw propeller.
Pressure cooling: After the melt enters the mold, maintain pressure to prevent backflow, and cool quickly to improve dimensional accuracy and molding efficiency.
Demolding and taking out parts: After cooling, open the mold and take out the pipe mechanically or manually.
Shaping and trimming: Remove excess parts such as flash and burrs to ensure that the welding interface size is compliant.
Advantages of injection molding
High production efficiency: Injection molding can realize automated continuous production, with large output per unit time, and is suitable for large-scale standard parts manufacturing.
Good dimensional consistency: The mold has high precision and small dimensional deviation of the finished product, which is conducive to improving the accuracy of welding butt joints.
Good surface quality: The surface of the pipe fittings is smooth and free of pores, and there is no cold material inclusion inside, which meets the sealing requirements of high-standard pipeline systems.
Flexible structural design: Complex internal and external shapes can be designed, such as reinforcing ribs, positioning grooves, etc., which are conducive to enhancing the connection strength and stability.
High material utilization rate: HDPE injection molding scraps can be recycled and reused to reduce production costs.
Other optional processes: turning and extrusion molding
Although injection molding is the mainstream method, HDPE socket pipe fittings may also use other processes in some special application scenarios, such as:
1. Turning (machining)
Suitable for large, non-standard customized socket pipe fittings or structural parts with high wall thickness requirements. Large-diameter HDPE hollow bars or solid bars are usually used to process the shape and interface dimensions on CNC lathes. Its advantages are strong flexibility and no need for mold opening, but the production cycle is long and the cost is high, which is suitable for small-batch customization.
2. Extrusion molding + welding assembly
For some socket pipe fittings with more complex structures, semi-finished straight pipe sections or curved pipe sections can be obtained through extrusion molding, and then assembled into complete accessories through cutting, hot melt welding and other processes. This method is suitable for the rapid preparation of special-shaped parts, such as eccentric reducer elbows, long radius elbows, etc.
Key factors affecting molding quality
Raw material purity: Avoid using HDPE particles containing impurities or excessively high proportions of recycled materials to prevent the mechanical properties of the product from decreasing.
Mold precision and mold temperature control: The mold needs to be processed by CNC, the surface finish of the mold cavity should reach Ra0.4 or above, and the mold temperature control within a reasonable range is conducive to stable molding.
Injection molding parameter optimization: Parameters such as injection pressure, injection speed, holding time, cooling time, etc. need to be adjusted according to different sizes and wall thicknesses to ensure full filling and no shrinkage marks.
Demolding process control: Avoid forced demolding to cause dimensional deformation or interface damage.
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